Rotating Capacitors with Spiral Groove Features for Hydrodynamic Gap Maintenance in Power Conversion Systems

Download or read book Rotating Capacitors with Spiral Groove Features for Hydrodynamic Gap Maintenance in Power Conversion Systems written by Ryan Patrick Knippel and published by . This book was released on 2019 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: A survey of rotary power conversion systems based on electrostatics shows favorable features in materials and manufacturing, but they lag the gap power density of electromagnetic approaches by orders of magnitude. Rather than trying to match the air gap power density of electromagnetics, this work pursues modes of maximizing the capacitive surface area while minimizing the dielectric gap present in electrostatically coupled systems. Utilizing hydrodynamic bearing structures integrated into the surface of the rotating capacitors, the dielectric gap may be maintained at distances approaching tens of microns over tens of centimeters up to speeds exceeding 30,000 rotations per minute. This approach eliminates the longstanding air gap field impediment to electrostatic systems by increasing volumetric power density. The ability of this mechanical approach to enable capacitively coupled system is demonstrated in two areas of power conversion, wireless power transfer and an electric machine platform. The wireless power transfer portion of this research culminates the design and implementation of a system of axially stacked rotating capacitors for wireless power transfer, known as a capacitive power coupler (CPC). This device delivered 700 W at 6.5 amps of excitation to the field coils of an 80 kW wound field synchronous machine. 6 stator and 5 rotor discs offset by 115 microns comprised each of the two 2.8 nF coupling capacitors, yielding a total capacitor length of 4.98 mm. This design achieved a gap/rotor diameter aspect ratio previously attained only in the MEMs community, opening the way for the development of a macroscale electrostatic mechanical platform. An axial flux PCB based electrostatic induction machine (ESIM) platform utilizing the principles of operation of, and tools resulting from the capacitive coupler was constricted. Structural models based on tensile tests of FR4 were developed to predict safe operation spaces of the ESIM. The final ESIM platform maintains an axial air gap of 57 microns across its 170 mm diameter rotor face (a 1:1500 aspect ratio) and delivers 2.4 W of mechanical power per facing pair of rotor and stator discs. This proof of concept machine provides the first strong mechanical base for future electrical optimization of these machines.